I see lots of comments from folks stacking KT34XAs and CC 402s on the
same tower. Wonder if anyone out there is running the XA/2 el KLM 40 in a
stack? How I
got to where I am is kind of a long story, but to make it short, I
started with an XA
at 55 feet that had a somewhat high swr (1.7:1). I then added a 2L KLM 40
about
8 feet above it with the booms at 90 degrees from each other. Fifteen got
worse with
the swr going up to 2.5:1 or so and no pattern. It also appears that the
boom on the
XA is interacting some with the 2L 40.
So I'm sitting here trying to decide what all I should do after I pull
them both down and
rebuild them. Here are some of the questions in my mind:
1. What kind of luck are others having with the same spacing? One of
KLM's brochures indicates that there should be 8 feet minimum spacing
between the two. Bruce says I'll probably see less intereaction with a
little more spacing. I wonder
how much I'd gain by going from 8 to 11 feet.
2. I wonder what things would look like in my original configuration of
the XA was
working right on 15? My guess is it would probably pull the frequency up
some
yet, but not as pronounced.
3. From what I have read in the archives, the CC 402 doesn't affect the
XA on 15 because it's resonant at 18MHZ instead of 21. Before I put up
the 2 El KLM for 40,
I was using a KLM dipole. Like the CC402, it worked well on 18MHZ and
terribly on
21. (I noticed little if any interaction between the dipole and the XA).
Based on this
I was rather wondering why the 2el is tearing up the XA on 15. I suspect
that one
clue is the fact that this older KLM uses a matching stub sort of affair
called
a maxi-match that makes a dc connection between the driven element and
the
boom. KLM has since replaced the feed system with a 1:1 balun and a
quarter
wave transformer made of 75 ohm coax.This isolatesthe driven element from
the boom. While I was catching up on the towertalk archives I saw where
Frank W3LPL repeatedly stated that he insulates his elements from the
boom partially to reduce interaction between the stacks. I plan to
replace the matching section with the new version.
About a year and a half ago someone out in California had purchased a 2el
KLM 40
and built a quarter wave matching section to feed it. If you read this
reflector, I'd like
to ask a few questions.
73 de Larry K7SV in VA (K7SV@Juno.com)
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